texts: Could stellar occultations be used to survey Kuiper belt objects?

texts:
The first hint we had as to the shape of Ultima Thule was via an occultation study using an array of small telescopes. Has anyone investigated the feasibility and effectiveness of conducting a survey campaign using the same technique?

Given that this was managed for an arbitrarily selected object in a window of few years, it would seem that, if you just wanted to do the same thing for as many Kuiper belt objects as you can manage, that you should be able to get similar data for a significant number of objects a year at relatively low cost.

Edit: the kind of project I'm wondering about would be targeted at getting detailed shape (e.g. what fraction of KBOs are contact binaries?) and size data. For example a line of a few hundred 0.5m class interments at 100m to km spacing.

Edit 2: I guess I kind of didn't actually say what the target of the survey would be. To clarify, the objective would be to collect fine detail on the shape of KBOs. E.g. how common are contact binaries?


texts:
Saturn's rings contain many moonlets that shape the rings of Saturn. The structures in the rings of Saturn around moonlets are similar to those in protoplanetary disks around newly formed planets, which makes me wonder if the material in the rings will follow a similar fate and form into larger bodies.

Will the material within the rings of Saturn eventually coalesce into moons, or are the rings of Saturn stable enough to last billions of years?


texts: Can Jupiter's bands be made out using a 15x70 pair of binoculars?

texts:
I have been getting mixed opinions on this. I have a 15x70 Pair of Binoculars. I have tried staring at Jupiter for several minutes with it, I was able to see the Galilean moons, in fact the last time was so long that I noticed the Moon's position changing a little bit.

But the glare of Jupiter is so high that I could not see the bands. Is it really possible to see any of Jupiter's bands using a 15x70 pair when the angular size is about 45 arcseconds ?


texts: Why did the moon have a distinct reddish edge tonight?

texts:
In Monterey, California, with a "half-moon" high in the sky at about 9 pm (2017-08-30), the moon had a distinct red outline on the outer edge of the NE quadrant; for awhile I saw it also on the outer edge of the SW quadrant.
I observed this phenomena from two locations, about a mile distant from each other.
I've never seen that before. What would cause it?
I took a picture of it with my camera, but you can't tell anything "out of the ordinary" from the image.
UPDATE
It's a clunky picture (I've been watching My Three Sons lately) - red not visible, fuzzy, and makes it like a full moon, but here it is, at any rate:


texts: Where do the symbols $\lambda$ and $\beta$ come from for celestial latitude and longitude?

texts:
I'm reading Episodes From the Early History of Astronomy, and the author mentions the system of celestial coordinates based on the ecliptic. In this system, the two coordinates are latitude and longitude, denoted by $\lambda$ and $\beta$. Where does this choice of symbols come from?
$\lambda$ is "l" like in "latitude", I guess. But why $\beta$?


texts: What happens if a white dwarf collides with a star like our sun or a red dwarf?

texts: Would it explode in a supernova or  will it form a new star?


texts: Correlation of planet sizes with star sizes?

texts: I did my own amateur Kepler data analysis in May of this year of data from Kepler.nasa.gov/Mission/ discoveries. I found a strong correlation between star size and planet size (percentages). 37 of the 44 planets confirmed (84.1%) orbiting M dwarfs were less than 2.0 R(Earth) with only one hot Jupiter. 129 of 241 (53.6%) orbiting K dwarfs were less than 2.0 R(Earth) with 9 hot Jupiters (3.7%). 196 of 517 (37.9%) orbiting G dwarfs were less than 2.0 R(Earth) with 49 hot Jupiters (9.5%). 92 of 213 (43.2%) orbiting F dwarfs were less than 2.0 R(Earth) with 23 hot Jupiters (10.8%). I would like to know how much of this correlation is probably real and how much is biased by the limits of the study? Biases I am aware of are the fact that the Kepler study is primarily of systems with "close in" planets, (only 90 of 1015 confirmed as of 4/1/15 are over 0.3 AU) and that only 4.3% of the "Kepler stars" are M dwarfs. I also see biases that might arise from the methods of confirming the planets (Kepler stars from 110 to 405 had planets confirmed by the "multiple candidate" method). It also appears that there may be a greater difference between K and G star systems than between G and F. Where can I find a more professional analysis of this type?


texts:
How to find acronym of specific catalog in SIMBAD database? For example, I want to select
stellar names, object types and all binary stars from "Stellar effective magnetic fields. II." catalog (Bychkov+, 2009; J/MNRAS/394/1338) via SIMBAD script page. How to do this?


texts: Keplerian Elements for the Moon and Earth around their Barycenter

texts:
So I'm looking to replicate the inner Solar System to a decent degree of accuracy. So far I've been utilizing the Keplerian Elements and Equations for the planets, as shown here. There is one issue with this though:

For the Earth and Moon, I only get the path of the Barycenter. This is great, but it means that the next thing I need is the Earth's and Moon's Keplerian Elements relative to their Barycenter. Now I can get the starting element values from JPL HORIZONS or the JPL Planetary Satellite Mean Orbital Parameters. However, I get a bit stuck on what the best way to evolve these values over time is.

I'm thinking that maybe the answer lies in utilizing the Longitude Rate (n) in the JPL Planetary Satellite Mean Orbital Parameters for approximate motion.

Does anyone have any solid resources I could utilize to determine a good solution to this problem (i.e. books/links)?

Also, just so I know, does a question like this actually belong here? Or is it more appropriate for Space Exploration?


texts:
For a single lens: we got

\begin{equation}
 u(t)=\sqrt{\left(\frac{t-t_0}{t_E}\right)^2 + u_0^2},\end{equation}

so the magnification is

\begin{equation}
A = \frac{u^2+2}{u\sqrt{u^2+4}} \end{equation}

Therefore the magnification for a single lens depends on three parameters: $u_0$ (minimum separation lens-source), $t_0$ (time where the magnification is maximum) and $t_E$ is the characteristic event timescale, which is the time it takes for the source to move with respect to the lens by one Einstein ring radius.

For a binary lens, however, the formulae of $u$ and $A$ above no longer hold. $A$ can be calculated for a point $u=(u_1,u_2)$ using numerical methods (Press et al. 2002) but, how is calculated $u$ for a certain time $t$? According to Tsapras (2018) $u$ depends on $u_0$, $t_E$, $t_0$ but also the angle $\alpha$ at which
the source trajectory crosses the binary axis, the mass ratio between the two components, $q$, and the separation between them, $s$, projected on the lens plane. ¿How these last three parameters come into play in the calculation of $u$ for a binary lens?


texts:
Strangely, there isn't a lot of information on Ceres on the internet. I want to know the specific percentages of its composition.

Thanks in advance!


texts: Why do different instrumental filters use different magnitude systems (Vega vs AB)?

texts:
Suppose I wanted to construct the spectral energy distribution (SED) of an object. Further suppose I observe this object through the 9 broad-band filters using the Subaru Suprimecam (just for an example) here: http://www.naoj.org/Observing/Instruments/SCam/sensitivity.html

As the statement below the table of broad-band filters says, the Johnson-Cousins filters (capital letters) are on the Vega magnitude system whereas the SDSS filters (lowercase letters) are on the AB magnitude system. I understand what these two magnitude systems are and how to convert between them.

My question is: what is the point of the two sets of filters being on different magnitude systems, one Vega and the other AB? It's not as if the Johnson-Cousins filter hardware physically has the Vega spectrum built into it, right...?

If I do aperture photometry on an I-band image and an i'-band image, will the first one return Vega magnitude of the object and the second return AB magnitude of the object, by default? And if I wanted to do SED fitting, then I need to be consistent such that all of my data points (even from other telescopes) need to be on the same magnitude system (e.g., convert the I-band Vega magnitude into an I-band AB magnitude)? (Or do that conversion first, and only then convert to flux units via $\nu F_{\nu}$ or $\lambda F_{\lambda}$).


texts: Time dilation due to the expansion of the universe

texts:
This is not a homework question. I want some help in being able to clearly perceive the expansion of the universe and the consequences thereof.

We know that the universe is expanding in an accelerated manner. It is my understanding that space alone cannot expand without affecting the local time. Thus as per GTR, depending on the curvature of space-time and the energy density, time too shall suffer a change due to the changing space.

Assuming that there is no curvature of space-time and no mass or energy contained in a chunk of space (assuming the zero point energy of empty space as zero) between two galaxies A and B, let us say that the local time at a point P in this space goes as $t_0$. If we on Earth could somehow observe this point and measure the time at P as $t$,

When we talk about the rate of expansion for example as in Hubble's Law, do we follow the comoving coordinates or the proper coordinates?
How would $t$ and $t_0$ relate to each other if the rate of expansion is uniform and accelerating respectively?
How much is 1s for the comoving observer at the inflation period in terms of the usual 1s now on Earth?


texts: How early/late is the human race as intelligent life in the universe/milkyway?

texts:
In the history of the universe, there has been a time, where intelligent life had no chance to develop (e.g. in the early universe, when no habitable planets have formed) and there is a time today where we know, that at least one intelligent lifeform has evolved in our universe/galaxy. Between these two times many events took place in order to provide the conditions, that (intelligent) life can evolve. So I wonder myself:

Considering the time, when the conditions in the universe became life-friendly, has the human race as intelligent life evolved early, late or something in between?


texts: Observational evidence for the existence of black holes

texts: What is the direct observational evidence that black holes exist? I have read that black holes have been detected through X-ray emission. What is some other observational evidence for black holes?


texts:
I understand the collapse of a star during a supernova, as the outward pressure cannot compete with the gravitational field.

Is it conceivable, that a relaxation of the space-time curvature is what expands the space and looks like an explosion?

I have often wondered, to extrapolate, if a "release" of the curvature of space itself, or in an extreme example a massive black hole releasing all of its potential energy in an instant (In a way not yet understood) could be in fact the (or a) big bang.


texts: Calculate the time when Arcturus passed through the meridian

texts:
If the observer observes Arcturus passed through the meridian about 23:00:00 of 28 April. Find the time that Arcturus passed the meridian in 29 April. And what day does the Arcturus will pass the meridian about 01:00:00?

I think that when Arcturus passed through the meridian, the hour angle will be 0 degree. Sidereal time equal hour angle plus right ascension. right ascention of any stars always be the same. So Sidereal time will be as same as every times while the star located at the meridian. And it doesn't matter because solar time equal sidereal time minus 12hr. Do I understand something wrong? And how do I do this question?

Adding question;

Your answer was very clear. But if I consider about the moon instead ex; the observer is at the equator and saw the moon which has a declination of 0 degree set at 11:00 PM yesterday, what time the observer will see the moon set today? I try to use the thinking process like this again. I know that the sidereal month of the moon is 27.32166 days. I calculate the solar month of the moon from 365.24219 of solar year divided by 12, and I get 30.43684 days per solar month. From subtracting both of these numbers, I get 3 days plus about 2 hours 45 minutes and 52 seconds. So to answer this question I will get 2 hours 45 minutes 52 seconds behind. My answer is that I will see the moon set at 13:45:52 PM. Do I right? I don't understand why the time I get is behind instead of earlier as the question about the Arcturus I asked before. I'm also not sure that does the declination of the moon and the position of the observer relate or not too. Thank you very much:)


texts: What fraction of starlight, seen from Earth, is actually reflected light?

texts:
Thanks to reflected starlight, many planets and comets in the Solar System have been visible to humans since long before the development of modern astronomy.

Some of the starlight from outside the Solar System should be reflected light as well. That is, light emitted by one star in the Milky Way may encounter another star, and be reflected toward Earth. Normally, stars are assumed to be perfect blackbodies, but in reality they must bounce off some radiation.

Also, starlight should be reflected off exoplanets, moons, asteroids, meteors, comets, brown dwarfs, etc. What fraction of starlight, seen by the naked eye from Earth, is actually reflected light?


texts: Are there simplified M-L, M-R, and lifetime equations for non main sequence stars?

texts:
To give some context - I am trying to create a simple program that outputs the stellar properties of a star when given its initial mass and current age.

e.g.

Input

Initial Mass = 2e30kg
Age = 4.6 Billion years

Output

Type = Main Sequence
Class = G2V
Radius = 7e5km
Surface Temp = 5778K

or

Input

Initial Mass = 2e30kg
Age = 10.2 Billion years

Output

Type = Red Giant
Class = K4V
Radius = 4e7km
Surface Temp = 4000K

My issue is that the equations I have used to calculate these output properties are only applicable to the main sequence so cannot be used for other types such as red giants, super giants, or white dwarfs (e.g. The Mass-Luminosity relationship).

I have not had any luck finding the equivalent equations after many hours of googling so I would really appreciate any help or even a google keyword I can search for to put me on track.


texts: Direction of movement sun with respect to the NGP

texts: When viewed from above, i.e., looking down from the North Galactic Pole towards the South Galactic Pole, does the sun rotate clockwise or counterclockwise around the Galactic center?


texts: Do photons slow down as they approach the event horizon of a black hole?

texts: So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)?  Do photons slow down at some point, or is it somehow binary, where at one moment they are moving at the speed of light and the next they aren't moving at all?  Or, do they continue to move at the speed of light, just never moving beyond the black hole?


texts: Length of a tidal day or by how much is the Moon late each day?

texts:
A tidal day is the MEAN time between successive meridian transits of the Moon. (This is sometimes called called a lunar day, a term that should be deprecated for use in this sense, because it is also used for the length of a day on the Moon and should be reserved for the latter meaning to avoid ambiguity.) Its length exceeds a mean solar day of 24 hours by X minutes, which is also the (mean) time-length by which moonrise (or its meridian transit) is later each day than it was yesterday. (Here is an animation by NOAA demonstrating this principle.)

The exact value of X is variously given in different places, ranging from about 48 to 52. However, I cannot find anywhere an authoritative source detailing the "correct" way to calculate X.

Does anyone know of an authoritative method of calculating X, and/or can anyone comment on the three methods given below.

(1) I have a personal theory that puts X at about 48.763 minutes, but I am uneasy about how correct the underlying logic of it is, which is this:

Consider two successive conjunctions (C1 and C2) of the MEAN sun and MEAN moon. At C1, the Sun's azimuth and the Moon's azimuth will, at ALL places on Earth, be the same, and, although this is no longer true for the rest of the lunation, it will once again be true at C2. This is analogous to two clocks: Clock 1 (the MEAN sun) keeps correct time, while clock 2 (the MEAN moon) loses a constant amount of time (X minutes) each day. Since the two clocks agree at C1 and at C2, clock 2 must have lost exactly 24 hours (1440 minutes) during the intervening synodic lunation, whose length (Ln) is 29.5305891203704 days. This suggests that X (the number of minutes that clock 2 loses per day) = (1440 / Ln) = 48.763.

However, I feel uneasy about this logic for this reason: If C1 occurs on April 1 at 06:00:00, UTC, and it is then sunrise at Tema, Ghana (on the prime meridian, near the equator), C2 will be on April 30 at 18:44:03, UTC, and that will not be sunrise at Tema; it will be dusk there, and it will be sunrise at east longitude 169°.

Does this negate the above logic suggesting that X = 24 hours / Ln?

(2) Another method for calculating X suggested to me is this:

It is based on the Moon's sidereal period (Ld), 27.321661 days. The MEAN angular distance along its orbit travelled by the Moon each day is (360° / Ld) = 13.17636° (which equates to a mean orbital speed of about 0.55° per hour.) So, each day, the Earth must rotate 360° plus an extra 13.17636° to point the same meridian back at the Moon again. The Earth's rotational speed is (360° / 24 hrs) = 15° per hour. At that rate, the extra time needed by the Earth to rotate those extra 13.17636° is [(13.17636/360) * 24] = 0.878424 hour = 52.7 minutes.

(3) I argue that even if method (2) is right in principle, it requires two amendments, because:

(a) The Earth rotates 360° in a sidereal day, which is nearly 4 minutes shorter than 24 hours, in which time the Earth rotates nearly 361°, or, more precisely, 360.98565°. (The fraction in the latter value is obtained from the average daily portion of the Earth's orbit: 360°/365.2422 days = 0.985647° per day.) (An animation demonstrating why this is so is here.) So, the extra time needed by the Earth to rotate those extra 13.17636° is:

[(13.17636/360.98565)*24] = 0.8760 hours = 52.56 minutes.

(b) Furthermore, in those extra 52.56 minutes, the Moon has moved on in its orbit by nearly another half a degree. More precisely, it is (360/27.321661)*(52.56/1440) = 0.48094°. So the calculation should be:

[(13.17636+0.48094)/360.98565)*24] = 0.90800 hours = 54.48 minutes.

So we have three different methods of calculating X, yielding values of 48.763, 52.56 or 54.48 minutes.

Comments anyone? Either endorsements or criticisms of any of these three methods will be gratefully accepted.


texts: Questions on dark matter observations in galaxy clusters

texts:
For cluster of galaxies we can observe velocity distributions and so we can deduce mass from multiwavelength observations. I suppose total mass of the cluster could be deduced by observing velocities of galaxies and applying virial theorem. Is it be done using general relativity or just with classical mechanics ?

An other way could be whith looking at gravitational lensing it causes on far galaxies.

Are these two methods giving same results ?


texts: How do I calculate the barycentric position of the sun at a given julian date?

texts: I have used the (matlab/octave) SOFA routine/function iauEpv00 to get the barycentric position and velocity of the Earth, but now need to find barycentric position of the sun. Can't seem to find the right routine/function.


texts: How to calculate phase angle of a satellite?

texts:
I'm making a program for predicting satellite passes. I'm trying to find out if the satellite is illuminated by the Sun and not in Earth's shadow. I need to know its phase angle: the angle between the observer on Earth, the satellite and the Sun.

Please explain it in simple terms if possible.

(Inserted by reviewer, extension to question, posted originally as answer)

I have TLE data for the satellite (contains right ascension). From that I got ECI position, azimuth, elevation, altitude. For observer I have latitude and longitude and for the sun: elevation and azimuth.


texts:
Suppose I have a 2D data array with number of counts in each pixel (i.e., this is the image array). Suppose I have another 1-1 mapped same-shape data array that gives the 1-sigma Gaussian standard deviation in the number of counts in each pixel in the image (i.e., this is the error array).

If I do circular aperture photometry, I just calculate -2.5*log10(summed counts within aperture) + magnitudeZeropoint.

On the other hand, for the magnitude uncertainty on my aperture magnitude, I read that I'm supposed to do a quadrature sum of the errors within my aperture, then compute the fractional flux uncertainty as the ratio of my quadrature-summed uncertainty divided by my measured counts from the image, and then magnitude error = 2.5*log10(1 + fractional flux uncertainty).

How come the uncertainties have to be quadrature summed ($\sqrt{\Sigma \sigma_{x,y}^2}$), instead of just added up like I do with the image pixel values? The quadrature sum results in a smaller errorbar but is that realistic? Also, I emphasize that my data arrays are in units of counts (i.e., ADU's), not electrons.


texts: Why pulsar pulses are so extremely regular?

texts: It's often said that the pulses of the pulsar have a very precise period, which helps to detect easily exoplanets that cause fluctuations in the time of arrival (TOA) of the pulses. Anybody knows why?


texts: Estimates of exoplanets distribution consistent with current data

texts:
I am interested in current estimate of distribution of planets of various radii in various distances from their parent star. There is many sources, where one can find database of presently known exoplanets, for example exoplanets.org, www.openexoplanetcatalogue.com and others. However, the known exoplanets are, of course, subject to conditional probability of detection by various methods. One cannot take the database as representative distribution, because, for example, hot Jupiters or big planets in general would be greatly overestimated.

What are the best resources to obtain current unbiased estimates of exoplanet radii and distances?


texts:
Given two colorindices LX and LY, such that the color X-Y is given by

X-Y = -2.5 log(LX/LY)

is there a way to infer the luminosity in X (or Y)? I'm think not because any information on units has fallen out through this definition, but I could be wrong. I'm just not sure how to compute the luminosity straightforwardly otherwise, as this color index is the only output (along with the distance modulus) from an interpolation scheme of stellar templates.

Help would be much appreciated.


texts: How did ancient astronomers know to order the planets from the closest to the farthest from the Sun?

texts:
If we assume a geocentric model of the universe (like ancient astronomers did) how could we ever find out (again, like ancient astronomers did) the right distances of the planets? For example, how did they know that Jupiter is
further than Mars, if Jupiter is brighter?


texts: Finding Asteroid Geocentric Longitude and Latitude

texts:
I started using the software that comes with Jean Meeus book Astronomical Algorithms. I am now using the updated code from naughter(dot)com/aa.html.

I am able to calculate the heliocentric longitude and latitude for an asteroid using the orbital elements. Below is for the asteroid Juno. I can't find any source code or instructions for converting the asteroid coordinates I calculated below to geocentric longitude and latitude. Can anyone recommend a method to find asteroid geocentric longitude and latitude? Thanks.

double Longitude = 0.0; //West Greenwich
double Latitude  = 51.4826; //North Greenwich
double TZOffSet = 0.0;

//Asteroid Juno Elements;   Using epoch J2000
CAAEllipticalObjectElements elements;

//Calculation Julian Date  2017, 9, 25
elements.JDEquinox = JD;

elements.T = (JD - 2451545.0) / 36525.0;

//semi-major axis of the orbit
elements.a = 2.6700912;

//eccentricity of the orbit
elements.e = 0.25498122;

//inclination of the plane of the ecliptic
elements.i = 12.98211;

//Longitude of ascending node
elements.omega = 169.91138;

//longitude of perihelion
elements.w = 248.10807;

//-------------------------------------------------------------------------
CAAEllipticalObjectDetails details = CAAElliptical::Calculate(JD, elements, true);

1) Heliocentric Ecliptic Longitude  = 215.6670202
2) Heliocentric Ecliptic Latitude = 9.377841131
3) True Geocentric RA = 13.90415220
4) True Geocentric Declination = -3.802673727
5) True Geocentric Distance = 4.136531368
6) True Geocentric Light Time = 0.0238906126
7) Astrometric Geocentric RA = 13.90397025
8) Astrometric Geocentric Declination = -3.80217202
9) Astrometric Geocentric Distance = 4.13653445
10) Astrometric Geocentric Light Time = 0.023890630
11) Elongation = 26.74464206
12) Phase Angle  = 7.928218201
//-------------------------------------------------------------------------


texts: What is meant by "there is no refraction at the zenith"?

texts:
Wikipedia states:

  Atmospheric refraction of the light from a star is zero in the zenith

and other sources seem to agree.

I don't see why this should be so. Consider a situation in which air gets warmer from left to right. Then light should curve towards the warm air, and a star at the zenith would appear refracted.

So why do so many sources claim there is no refraction at the zenith? What do they mean by this?


texts: What is a quaternary mirror and why does the E-ELT need one?

texts:
In this recent BBC article I read the one-sentence paragraph:

  "Development on the mirrors - in particular, a very complex quaternary mirror - continues apace."

and became interested in the following questions:

What is a quaternary mirror
Why does the E-ELT need one
What is it about this mirror that is "very complex"?

note: the E-ELT is the European Extremely Large Telescope nearing final design, and to be installed in Chile's Atacama Desert (host to many other telescopes).

A drawing of the E-ELT from from Wikipedia (note scale of humans):

An image from the BBC article:


texts: Are neutrinos affected by gravity fields?

texts: Am asking if a neutrino can be pull by the gravity field of a quasar or a black hole, assuming the neutrino have momentum. It could be possible in the that a neutrino can orbit a black hole at an orbit equivalent to the Schwarzschild radius give or take. If it even possible for a neutrino to go through a black hole?


texts:
From my research, I found out that quasistars theoretically existed because of a black hole core whose radiation pressure counteracted gravity within the star. However, a few websites stated that quasistars do not exist now because there are metals contaminating hydrogen and helium.
Could somebody explain to me why metals (or a small displacement of hydrogen and helium) would influence a black hole's radiation pressure, or is it just that there's no where that that much mass (1000+ solar masses) can exist anywhere in one place now?
I looked on Wikipedia (I usually do this and then research on different websites if I find something interesting there) and here1.


texts: How many Moon's Topocentric Conjunction occurs per lunar month?

texts:
It is clear that only one Moon's Geocentric Conjunction occurs per lunar month, what about the Topocentric Conjunction for a given location?

without scale I can imagine many Topocentric Conjunctions as shown in the pictures below:

yellow disk : Sun
gray disk   : Moon
blue disk   : Earth
yellow box  : Observer's Location
red line    : Conjunction's Line


texts: What would happen if you jumped out of a moving spacecraft?

texts:
I've watched a film where one of the characters claimed to have rapidly disembarked a moving spacecraft during a 5g burn (?!) and immediately wondered how he survived.

For example, you're on a spacecraft that's travelling at 100mph (or any other random speed) and you go to the nearest airlock and jump out (I.E: leave the spacecraft).

Assuming you have a strong enough protective suit (I.E: this isn't a murder/suicide):

What effect does this have on your body?
Does the vacuum of space mitigate or exacerbate the negative effects?
Will you just "float out" into space or will you actually be moving with/in the general direction of the spacecraft?
Do you slow down or speed up relative to the spacecraft?
How do the effects change as the speed changes?

I apologise for the multi-part question, but this question can't really be summarised in a single sentence.

UPDATE: Also, has this ever happened before? Has anyone ever "fallen out" of a spacecraft and made it back safely?

Thank you.


texts: Can a single location on earth witness solar eclipse totality 2 times during a single eclipse event?

texts:
The question came to my mind when I saw a visualisation of the path of the moon (relative to the sun - the sun is kept centered in the graphic, and only the moon moves) as its seen from a particular location during a solar eclipse.

This reddit post has the visualisation - https://www.reddit.com/r/delhi/comments/h0u878/in_10_days_there_will_be_a_partial_solar_eclipse/

In the visualisation, the moon appears to move towards the sun, and then retraces its path (almost).

If the moon crosses the sun, and then makes its way back, it is possible for the moon to cause 2 totality events at the same location on the earth.

Is this actually possible? Why or why not?

Has it even happened in the past? When and in which location?

When and where will it happen again?


texts: What is the magnitude of variation of Earth's orbital inclination?

texts:
Please excuse if this has been asked and I just didn't find it.

I have found several references that indicate that the inclination of Earth's orbit varies over a period of ~70,000 years, but I can't seem to find anything that tells what the range of variation is. I know that it's currently at 1.57° to the invariable plane, but I'm looking for the value of the maximum tilt.

Thanks in advance!


texts:
After reading about the Earth's orbit and how it moves faster in January than it does in July (based on its distance from the Sun), I started to wonder...

How far does the Earth travel around the Sun during each month of the year?

What is the math behind this calculation?

Note: I'm not asking about the average monthly distance, but the unique distance traveled for each month.


texts: Would a black hole passing next to a star create a deadly focal point due to gravitational lensing?

texts:
Black holes bend all kinds of radiation thanks to their giant gravity. Now imagine that a black hole passes close to some star (we know of cases when black hole devours a star). Star emits massive amounts of radiation in all directions, so naturally the radiation just outside the event horizon will be bent by the black hole. Many rays will be focused into a single point.
Wouldn't that create a "certain death zone" on the opposite side? Could this be a real threat for celectial bodies from far-away black holes (for example for earth)? If this effect in fact happens, would different radiation types be focused farther away - for example UV, visible, X-Ray etc. in it's own zones (EDIT: meaning basically - do black holes work similar to prisms by lensing different types of wavelengths differently)?

In the draft above the yellow circle is a star, black dot is black hole, gray circle is event horizon and red circle is the "death area where rays are focused by the black hole


texts: How to determine when Sun/Moon is aligned to two location on Earth's surface?

texts:
I would like to make a photo to Moon/Sun when it is very low on horizon, so if I make the shot far away from an object on Earth surface, it appears as big as the Sun.
But how can I calculate the right moment? Any site or app? Could NASA Horizons help? I made a GUI for it, but don't know if any quantity I can query could give me the information  I need:
http://win98.altervista.org/space/exploration/NHUGUI.html


texts: Gravitational wave detection time difference between LIGO Livingston and LIGO Hanford

texts:
Quote from LIGO's news release:

By looking at the time of arrival of the signals—the detector in
Livingston recorded the event 7 milliseconds before the detector in
Hanford—scientists can say that the source was located in the Southern
Hemisphere.

GPS coordinates of LIGO Livingston: 30.5630018,-90.7763949
GPS coordinates of LIGO Hanford: 46.4554032,-119.4092701
Distance: 3030.13 km
Now if the gravitational waves propagate outwards at the speed of light a difference of 7ms implies the following maximum possible detector distance:
299792458 * 0.007 / 1000 = 2099 km

Where am I wrong ?
Update:
As pointed out by james-k in the comments below, the calculated 2099 km is the minimum distance and not the maximum ... these waves seem to have caused some mental derangement ;)


texts:
Was universe spawn from nothing?
Until now, scientists figured out that the Big Bang happened from a tiny particle which was infinitely energy densed and having infinite mass. If that is the case where does that particle came from? Whats the current explanations based on current knowledge?


texts:
Apparently EGSY8p7 is the object with the longest light travel distance, 13.2 gly or a redshift of z = 8.68 (Wikipedia).
So the light took 13.2 billion years to travel to us from that object, but we know that the universe has expanded since (I believe with an expansion rate that varied over time). So given our current theories of how the universe expanded, is it possible to calculate the theoretical distance of that object to us right now?

I assume it must be close to what is believed the radius of the observable universe (46.5 Gly) but how would one go about to calculate this?


texts: Approximate distance from Earth to Mars at a given moment with reasonable (+/-100km) accuracy?

texts: I've been scouring the internet for a straightforward way to approximate the distance between Earth and Mars at a given time. I hope to achieve an accuracy of about 100km.


texts: Is the gravity on Kepler 39b higher than on the Sun?

texts:
According to the formula for gravitational acceleration $a = GM/r^2$ where $G=6.674 \times 10^{-11}$, Jupiter with mass 1.89813 × 10^27 kg and radius 69,911,000 m gives a gravity around 25m/s^2. The Sun with mass 1.989 × 10^30 kg and radius 695,510,000m will have a gravity around 270m/s^2.

But using the data for Kepler 39B, mass 18 times that of Jupiter 3.416634 × 10^28, and radius about 5/4 of Jupiter's 87,220,000m, I get almost 300m/s^2, higher than the Sun's.

Is this right?

I did and redid it, and still concerned that I am doing something wrong.


texts: How do we know that light is redshifted/blueshifted and not the original light of a star/galaxy?

texts: If a star/galaxy is moving towards us, then its light is blueshifted, and if it is moving away from us, then its light is redshifted. How do we exactly know that the color we are seeing is not part of the fuel burnt by the star/galaxy, and is instead caused by the Doppler effect?


texts: How is the mass and semimajor axis of a directly imaged exoplanet found?

texts:
I can't find information on this for the life of me.

How do astronomers approximate the mass and semimajor axis of a directly imaged exoplanet? Would several photos need to be taken to find the period and find with Kepler's third law or can it be inferred through the temperature of the planet (or another method)? Also if you have any sources of this that would be great.

Thanks


texts: Who first hypothesized that the universe is accelerating?

texts: I couldn't find this answer anywhere.  Before 1998, was there a notable physicist who conjectured that the universe is accelerating and perhaps even submitted some equations to support it (and the existence of dark energy).  Such a hypothesis would likely have been rejected outright and fallen into oblivion, which is why I have to ask this question to get the answer.  And I don't mean Einstein's cosmological constant since he was trying to make the universe static rather than accelerating.  Someone who actually believed that the universe's expanding rate was increasing even before there was any evidence of it.


texts: Delta Velorum - non-observed variable star

texts:
I am a beginner variable star observer from the Southern Hemisphere (but with experience in astronomy) and, when I was looking for VS to observe, I saw that Del Vel has almost no observations. Thus, there is no graph for when the eclipses occur.
VSX data: mag range of 1.95 - 2.43 V, period  of 45.15 days and 1.3% (0.587 days) eclipse duration
It doesn't have data about how the magnitude varies in the visual spectrum, althought I know it is a bright star (already saw it at naked eye).
Does it vary in the visual spectum, or there simply is no data enough to determine this? Could I collect this information visually, or is this waste of time?


texts:
Two days ago I went to a mathematics conference where there was a paper presented on Jupiter's formation via the disk-instability model.

I know that there are two different theories for the formation of the planets. One of them is the Core accretion model and the other one is the disk-instability model. I also tried to read this paper on planetary formation in which they said 161 planets were put on to test. 90% followed Core accretion model and rest of them followed the later model. Did not say anything explicit about Jupiter.

Jupiter is too close to the Sun to follow the Disk-Instability model (I am not sure completely).

Now I want to know which model Jupiter follows for its formation.
(I asked this question on physics stack-exchange too but unfortunately there were no answers)


texts: How can something infinitely big have expanded from an infinitely small?

texts:
Please help me reconcile what I see as contradicting theories:

The universe began with the Big Bang and expanded from an infinitesimally small point.
The universe is infinite.

How can something infinitely big "expand" from an infinitely small point? There has to be some sort of a 'blast wave', right?
Also, if we think we know the total amount of matter the Big Bang must have produced - how can a limited amount of matter fill an infinitely big universe?
P.S. One idea I have is that the universe may be infinite, but the Big Bang didn't create it - it created matter within the infinitely big universe. This would explain the expansion we're observing now: the matter will continue being distributed across the infinitely large universe. So I guess my question is more of a "why this assumption is incorrect"... :)


texts: Delay of Moon passing a defined meridian each day

texts: On the website Lunar Synodic Curve a nice image of an Moon analemma is shown together with an explantion on the reason why for the different phases of the Moon the images have to be taken with 24h 51min apart. It is explained that this difference is due to the longer synodic month of 29days 12hrs 44mins (compared to the sidereal month of 27days 7h 43mins). Whereas the explanation that due to the additional rotation time for the moon to reach the same angular relation to the sun an additional angle of 29.1 degs has to be travelled, the last step to come to the additional 51mins each day is not clear to me. Any clues on how to calculate this from the sidereal and synodic month duration or the associated mean motions of moon and sun would be very welcome.


texts: Will universe's lakes get boiled by the CMBR?

texts:
From what I can understand, Cosmic Microwave Background Radiation (CMBR) is microwave now, but was initially visible light emitted long time ago.

The microwave is producing a wave that’s about 12 centimeters long.
Now CMBR has right now this (time changing) distribution (peak at 2mm):

By Quantum Doughnut - Own work

This diagram was created with gnuplot., Public Domain, Link

So it looks to me that in some time, when its wavelength falls at around 12cm), some of its energy should be transferred to water molecules the way it is in a microwave oven.

Is it the case? Will some of the CMBR energy actually transferred to water molecules?
Will this energy be too faint to matter at our scale?


texts: Jupiter-Venus conjunction is vertically aligned. I'm at 49° N. How is this possible?

texts:
The very beautiful Jupiter Venus conjunction of ~ 2019-01-20 (practically something out of "2001 A Space Odyssey") is seen as "vertically aligned" in the dawn sky, Venus "above" Jupiter.

See this picture by Jeff Majewski at EarthSky.com to see what I mean (not sure I can copy it in here directly)

This should mean my "vertical" is aligned with the Ecliptic. I'm in northern latitudes (49° N), how is that possible?

And is this alignment geometrically linked with the "Super Wolf Blood Moon" which was very visible at the same time?

Update

The problem seems hard to explain so here is a little free-hand drawing.

The observer sits on the equator and is just being moved into sunlight by Earth's rotation (the image shows Winter Time for the Northern Hemisphere). The observer's "UP" vector lies in the Ecliptic Plane. This being so, and Jupiter and Venus also being in the Ecliptic Plane, the observer can see Jupiter and Venus aligned "vertically" (same azimuth), separated by a couple of degrees in elevation. As the day progresses, that vertical alignment will evidently cease as the line connecting the planets rotates relative to the observer.

This works on the Equator, but what if the observer is at higher latitudes? I can't get my head around the idea that the planets can be vertically aligned while still being on the Ecliptic Plane.


texts: Could the Sun's planetary nebula be dangerous for the planets?

texts:
Since the Sun's mass isn't high enough it won't go supernova being a red giant but instead release a planetary nebula. So that seems to be kind of a substitute for a supernova. Would ejecting the planetary nebula be any dangerous for the planets of this system or maybe even other planetary systems close to the Sun?

I mean, the Sun releases its outer layers forming a planetary nebula. What remains is essentialy the Sun's core and will collapse to a white dwarf. What if the released matter (outer layers of the Sun) collides with a planet or moon?


texts: Is there a upper limit to the number of planets orbiting a star?

texts:
Our sun has 8 planets orbiting as well as a number of dwarf planets. Are there any calculations that hint as to whether this number is close to some theoretical maximum value or are we simply an average solar system in this particular way?

I could imagine that if you have many planets, they will likely interact with each other. Can you calculate any theoretical value for the maximum number of planets which have long-term stable orbits around their own star?


texts: New NEOs are found daily. Is there any evidence gravity is pulling them to a centralised location?

texts: With all of the new NEOs (near-earth objects) are they being pulled in or are they interacting with each other?


texts: After reading this space timeline, I have wondered how they managed to make these assumptions about various events like when the first black holes formed. This is obviously far beyond the good ol' carbon-14 dating procedure.


texts: What are the azimuths of the planets' orbits?

texts: I am creating a virtual solar system model and I want it to be as realistic as possible (e.g. orbits are ellipses, not circles, and orbits are oriented correctly, not all coplanar).  In order for me to do this, I need to know the eccentricity of the orbit, the perihelion, the semi-major-axis, inclination and azimuth.  I have all of this information, except for the azimuth of the orbit, which is the angle from the sun to the aphelion.  Are there any reliable sources with this information?


texts: What is the angle of precession of the star S62 orbiting the Milky Way supermassive black hole?


texts: What is the projected range of the JWST to be able to detect exoplanet atmospheres?

texts:
Yesterday the K2 mission detected transit events of objects passing in front of a number of M dwarfs which could turn out to be rocky planets. If some of these planets host atmospheres, could the JWST detect IR absorption lines from molecules in these atmospheres?

What would be the expected limiting distance for these stars to allow for such measurements by the JWST?


texts:
My question is simple:

Given the gravitational relationship between Earth and the moon, how wide is Earth's roche limit?  How close does the moon have to orbit before getting disintegrated by Earth's gravitational pull, and how far does it have to orbit before being free from Earth's orbit entirely?


texts: Calculation to Convert from Equatorial to Heliocentric coordinate systems

texts:
Can anyone help me with the formulas to convert Equatorial coordinates (Right Ascension / Declination) into Heliocentric coordinates (Angle and Distance in relation to the Sun) ?
i.e. Ra/Dec of 6.7659/18.4563 ---> 281.98 degrees and 0.4562 AUs
It feels like this is possible with no other inputs, but I can't figure it out.


texts: Will you be able to see the corona in a 90%+ partial eclipse?

texts: I live in Champaign, Illinois (see map) and am planning to watch the August 21st solar eclipse. This community is within the 95% totality range, but not within the path of totality. Will I be able to see the Baily's beads, and more importantly will I be able to see the corona?


texts:
I found this at
http://www.nature.com/news/the-exoplanet-next-door-1.11605

  Even when launched by one of the most powerful rockets on Earth, boosted by a gravitational slingshot around Jupiter, and further accelerated by a radioisotope thruster, that probe would take about 28,000 years to reach α Centauri. Quoting British author Douglas Adams, McNutt quips: “Space is big. Really big.”

Is this still the fastest we can get right now?


texts: How Good Are the Upper Limits on Heavy Elements?

texts:
There are between 90 and 254 stable nuclei all the way up to element number 82. In discussions and graphs about big bang nucleosynthesis nothing above lithium is even mentioned. It's a pretty safe bet that none of the heavier elements have been observed in reasonably primordial gases, since the implications would be profound enough to require mention in even popular level books about the big bang.

That said, has anyone bothered to perform searches for all of the heavier elements? As in, do we have explicit experimental upper limits on the concentrations of some or all of these heavier elements, or just a more qualitative, "No evidence seen for anything else"?


texts: How are solar systems found again after being discovered?

texts:
Discovering a solar system that cannot be seen by the naked eye on earth seems like an easy task with telescopes (e.g. the hubble telescope). I'm guessing, that our sun is the reference point for the bearing of the telescope at the point of discovery of a solar system.

But how do you find this solar system again? F.e., after discovering a "new" solar system, a year passes by, and there is need to know in which "direction" this solar system is in relation to ours.

A bit off-topic, but a reason as to why this question might be important: In science fiction there is often the possibility to travel faster than light, reaching other solar system quickly - or for the sake of this question lets assume, we would be able to travel there too in a timely manner. How would they/we know where to go, since the universe is ever expanding.


texts: Could we verify the structure of a black hole by observing an orbiting object?

texts:
Can we determine the physical structure of a black hole by observing its gravitational effect on objects in orbit?  There are three possibilities that I see, and would like to test:

Singularity at the center - The traditional view that there is a singularity at the center (e.g. all mass is concentrated in the center).
A structure where the black hole is filled throughout with matter inside the event horizon - My proposal, due to gravitational time dilation slowing / stopping time (e.g. a singularity will not form until an infinite amount of time has passed).  If the answer to my question on this subject here is correct, we should observe either possibility 2 or 3:  Does matter accumulate just outside the event horizon of a black hole?
A hollow shell, with matter only on / near the outside edge of the event horizon - My proposal, combined with the "vapor bubble" behavior, as hinted at in some of the answers to the linked question.

Would these three possibilities differ gravitationally in ways that could be observed (e.g. by observing orbiting stars), or would they be identical from the outside?  If they would produce different results, I would love to see what result it is that we actually observe!  We have observed stars orbiting the super massive black hole at the center of the galaxy.  http://scitechdaily.com/astronomers-discover-star-orbiting-the-black-hole-at-center-of-the-milky-way/


texts: How long does it take to produce a star? Why does it take that long?

texts: I wonder, why stars take a really long time to become stars? Is it because it needs to gain mass? Or heat up? Something like that? And could it be sped up at all?


texts: what magnification is required to see jupiter, saturn, venus and mars with a 50mm refractor scope with f/12 ratio and 600mm focal lenth

texts: i have a beginner telescope of 50mm and want to see planets it is arefractor with f/12 ratio and two eyepieces of 5mm and 10mm and i want to see mars, Jupiter, Saturn and venus. my max zoom ix 120x and focal length is 600mm


texts: On the geodesics of the metric $ds^2=-\rho^2d\alpha^2+d\rho^2$ and the constant $l=\rho^2\frac{d\alpha}{d\tau}$

texts:
In my assignment I have to deal with the 2D spacetime metric $$ds^2=-\rho^2d\alpha^2+d\rho^2.$$ During this assignment we have shown that the constant $$l=\rho^2\frac{d\alpha}{d\tau}$$ is a constant along the geodesics in that space. After this we found an expression for $\rho$ in terms of $\alpha$, for which $\rho(\alpha=0)=l$, namely: $$\rho(\alpha)=l\frac{2e^\alpha}{e^{2\alpha}+1}.$$
We plotted this function for various values of l, which gave:

Finally, we showed that in the close neighbourhood of the Schwarschild radius, i.e. $0<r-r_s\ll 1$, the metric $ds^2=-\rho^2 d\alpha^2+d\rho^2$ corresponds to the metric $ds^2=-(1-\frac{r_s}{r})dt^2+(1-\frac{r_2}{r})^{-1}dr^2$.

Now what we need to do is, use the result that the metric is approximately the schwarzschild metric at the schwarzschild radius to interpret the plots we found in the figure shown above and give a possible interpretation for l. And I really have no idea how to interpret these figures or what l might be.

Any ideas are welcome!


texts: Is there a way to tell the difference between earth andesite from Mars

texts:
I'm curios if there is a way to test if this sample might be Martian andesite.

What type of oxygen isotope (or other) test can be done to address this in some way?

As background, any information about such tests at the University of Utah would also be helpful to know.


texts: Why do speed of molecules increase when temperature is increased?

texts: Why do the speed of molecules increase when temperature is increased? Why don’t they burn and become ash? If it does happen that way, why does it happen after a certain level?


texts: Could human life thrive on a planet in a pulsar star system?

texts:
Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12.Two of the planets were the size of Earth.The pulsar observed by Spitzer, named 4U 0142+61 spotted a warm glowing disk formed from debris, The disk has a orbit of about 1 million miles and contains 10 Earth mass materials. Deepto Chakrabarty of the Massachusetts Institute of Technology, principal investigator states "Pulsars emit a tremendous amount of high energy radiation".

In a pulsar star system, could human life thrive on a planet with high energy radiation? If answering the question, please provide the latest references to date that are relevant with your statement.


texts:
The Ligo website says "Detecting the relic gravitational waves from the Big Bang will allow us to see farther back into the history of the Universe than ever before."

I find this puzzling. How can a Gravitational Wave originating at about the same time and place as the particles that make up their detector (ie in the Big bang) be detected?
To use a simple analogy - an explosion in an electronics warehouse causes a flash of light and pieces of electronics gear to be scattered. These pieces are then assembled to make a camera which is able to photograph the explosion. I am confused!

Answers suitable for a high school physics class greatly appreciated.


texts: How many exoplanets have been found around binary stars?

texts:
This XKCD whatif talks about circumbinary and [the other kind of] exoplanets. How many such exoplanets have actually been discovered?

I tried to look it up at exoplanets.org, but didn't find a column mentioning if the star is a binary.


texts:
How exactly, with steps and math shown, do you derive the masses of asteroids via perturbations? please, no links, because I have searched and searched for years and can't find anything.

I mean like asteroids- how are their masses determined exactly? What equations are used?


texts: We send a lot of rovers to Mars, as interesting as the planet could possibly be.  But why are we not putting satellite grids around planets that could transmit superficial probe data at the very least?  That seems to me like a much more interesting project.


texts: Who gets to name Planet Nine if it is confirmed?

texts:
According to Wikipedia, "On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech announced calculation-based evidence of a massive ninth planet in the Solar System."

If visual evidence or another researcher confirms the existence of Planet Nine, does the actual discovery warrant naming rights, or would this go to our Caltech friends?

I know from this question's answer, that:

  "Since the beginning of the 20th century the IAU is setting the standards for naming celestial bodies including planets. However, the IAU doesn't set the names, it only sets the standards."

Does the 'discoverer,' or the 'confirmer' get to name (theoretical) Planet Nine?


texts: How can you determine the distance of a star using the magnitude equation?

texts:
In high school we are undergoing a short course about astronomy. It is stated that you can use the apparent and absolute magnitude (m, M) to get a distance (D) of a star, with the formula
$$m - M = 5 \times \log(D) - 5$$
From which you free D:
$$D = 10^{\frac{m-M+5}{5}}$$
But how do you get both the m and M in practice, without knowing anything else? I can't imagine it.
I have asked my teacher but his explanation did not make sense to me, and as such I already forgot it.
Scenario:
you have a satellite which can measure the incoming photons  of a star. You now calculate the apparent magnitude using the formula:
$$m = m_\text{ref} - 2.5 \times \log(\frac{I}{I_\text{ref}})$$
Let's say you have a stable reference star and so you get $m=2$.
This is a nice start, but to determine the distance of the star you still need the absolute magnitude. How can you precisely acquire that using a HR-diagram? Because all the HR diagrams I have seen have a very fuzzy curve, and one temperature may map to multiple M.

This is what I'm struggling with: let's say you are somehow able to precisely measure that the star is 7500K. That means M can range from +4 to 0 (I guess we're also assuming it's a main sequence star, which we may not actually know), which gives us a possible D of about 4 to 25 (parsec?), which is an absolutely humongous range.
This can't be right, can it?


texts: Help understanding ring diagram analysis used in helioseismology

texts:
I need help understanding something. In global helioseismology we study the modes directly (stationary waves characterized by 3 integers numbers: $n$, $l$ and $m$). As the angular degree $l$ becomes bigger, the acoustic waves don't form a stationary wave (mode) anymore (they don't have enough lifetime anymore).
But, I'm working with ring diagram analysis (one of the techniques of local helioseismology) for these waves that don't form a mode. And in the data we still have and integer number $n$ (number of nodes in radial direction) and a non-integer number of $l$ (because the wave is not stationary).
I don't understand, what does that mean?? I have an $n$ and $l$ describing a propagating wave? What is the physical mean of that?

https://iopscience.iop.org/article/10.1086/306765/fulltext/38895.text.html
https://www2.mps.mpg.de/projects/seismo/NA4/NiceMeeting/proceedings/antia/electronic/ring.pdf


texts: Probability of planets in binary star systems?

texts:
There is much fiction on binary stars with planets, for whatever reason, and this keeps supporting the popular impression that those systems are frequent. Indeed,  the methods for identifying exoplanets and binary stars are somewhat the same. Are there actual observations of a binary star system with at least another planet (habitable or not)?
I know that binary star systems are rather frequent, and I am wondering whether there is any hard-science based statistics on how probable it is that systems of two or more stars have planets? As non-expert, I have the impression that not all configurations of binary star systems seem to be in favor of planets, see e.g. Roche lobe.


texts: What would happen if a person was out in space? would they get picked up by the pull of gravity from inbetween our planets, or sun?

texts: I'm curious, if someone were to be floating out in space. Would they eventually be captured by the gravitational pull from another planet or sun. To be more specific the person isn't anywhere near said planet or sun they are just passing between them. My question, is there some sort of current in between planets or sun that can have the slightest effect on an object passing through?


texts: Leonid meteor showers and the Tempel-Tuttle comet

texts:
I've been reading about the Leonid meteor showers and am struggling to understand one piece of information. On Wikipedia (Tempel-Tuttle), it states:

  The orbit of 55P/Tempel–Tuttle intersects that of Earth near exactly,
  hence streams of material ejected from the comet during perihelion
  passes do not have to spread out over time to encounter Earth. This
  coincidence means that streams from the comet at perihelion are still
  dense when they encounter Earth, resulting in the 33 year cycle of
  Leonid meteor storms. For example, in November 2009, the earth passed
  through meteors left behind mainly from the 1466 and 1533 orbit.

Why are we going through the meteors left behind by the orbits from 1466 and 1533? What happened to the orbit of 1500 and every subsequent orbit?

My guess is that the perihelion moves slightly from orbit to orbit so the earth moves through a different one each time but I'd love to get an expert explanation!


texts: why does pluto have a high orbital inclination

texts: Pluto has a high orbital inclination compared to the planets in our solar system.  What has caused Pluto to have such a different orbit -- was it always like this, or did something happen to make it so?


texts: Could the Philae comet lander be recharged by laser?

texts:
Could the Philae comet lander be recharged with a laser (or possibly many lasers) from earth?  My thought would be to aim one or more powerful lasers from earth at the Philae lander to recharge it through its solar panels.

Another thought would be to heat up a small part of the comet with one or more lasers, possibly causing the comet to slowly rotate into a position where the sun light falls onto the lander.

Would either of these ideas be feasible?


texts: Telescope magnification compared to distance from an object

texts: I'm looking at Saturn through a modest telescope at 50x. What point in space, expressed as the distance from Saturn, let's say it's 750 million miles from Earth, would I need to view Saturn with the naked eye and see it at the same apparent size as viewed from Earth at 50x. How do I estimate this in general for other objects as well. Thanks!


texts:
Narrators of astrophysics documentaries constantly state that matter spirals into black holes as if it were intuitive that this would happen because of gravity. But the moon isn't spiralling into the earth. Newtonian physics suggest that an object would either fall past the event horizon in less than half a revolution, or it would orbit indefinitely until acted upon by a third party.

Why would an orbit gradually degrade?


texts: Do we have knowledge of the geology of the moon?

texts: With reference to the Ebb and Flow lunar satellites, was there any data about its geology? Is there a central core, or is it homogenous?


texts: Why is twilight longer in summer than winter and shortest at the equinox

texts:
I recently decided to set my alarm clock to wake me up when it is "dark" out.  In the end, I decided to set my clock to the earliest time that nautical sunrise is in my state (Illinois) and stick with that all year.

While doing some research for this, I noticed something that surprised me.  Check out this disparity between astronomical sunrise to civil sunrise for the solstices and equinox (the latter two adjusted for daylight saving time):

Date/Astronomical/Civil/Disparity

Dec 20: 0533 - 0640 (67 minutes)
Mar 20: 0526 - 0630 (64 minutes)
Jun 20: 0320 - 0451 (91 minutes)

To be honest, these sets of ranges surprise me for multiple reasons.  I clearly don't know what I don't know, but here are some questions I can formulate:

Why would twilight be longer in summer than winter?  Before seeing this data, I had assumed that since the sun makes a more perpendicular path through the horizon in summer that twilight would be shorter in summer than in winter.  After all, in winter the sun takes a "slanted" path across the horizon.  Wouldn't the summer's path be more direct and therefore quicker?
OK: seeing this empirical evidence I conclude that something is wrong with my premise that forms my first question.  Summer twilight is longer in summer than winter.  However, I still would have assumed that March 20 would have had a twilight length in between the two solstices.  But it's not!  Why does the equinox have the shortest twilight?

Appended 5/13/2014:

I didn't want to leave my original incorrect statement in here without flagging it. As Cheekhu points out below, the sun does not follow a more perpendicular path in summer than winter, as I had erroneously assumed and stated above.  See his post for more details.


texts: Determining needed exposure time given SNR

texts: I need help on how to estimate an exposure time for a desirable signal to noise ratio (SNR). For example, given the magnitude and a desired SNR of a star we want to achieve, how long should the exposure time be? We may assume that the noise is only due to counting statistics, and ignore dark and flat noise. Any useful function to make this estimate?


texts:
Retrograde motion is:

  The apparent motion of the planets when they appear to move backward (from east to west) from the direction that they move ordinarily with respect to the stars.

Can planets inside the Earth's orbit around the Sun appear to undergo retrograde motion?


texts: Why is Mars considered the outer edge of the "goldilocks zone"?

texts:
In both books and documentaries I often see the Goldilocks Zone as described between Venus and Mars with the Earth "just right." This seems sort of ill thought out to me, because it assumes that Venus' atmosphere comes from its distance from the sun and the same with Mars. I'm not too familiar with current ideas about how Venus' atmosphere formed, but with Mars I'm fairly sure it's widely understood the reason the atmosphere is so small is because the gravity is so weak. Even some discussions about terra forming Mars mention that within a few million years, perhaps, the atmosphere would drift off into space.

So how can we be so certain that's the limits of the zones, especially with Mars? If Mars was as large as Earth/Venus and could hold on to a thicker atmosphere and thus retain more heat, then wouldn't that automatically push out the Goldilocks Zone? It seems like the edges have been places arbitrarily without consideration as to why they're the edges instead of "they just are." This comes up especially because even with its weak atmosphere, at the equator, it can reach up to 20 degrees which is well within the realm of liquid water.


texts: How to convert theoretical template spectrum from luminosity density to flux density units?

texts:
I'm working with galaxy spectral templates (e.g., Bruzual & Charlot 2003) which seem to always come with y-axis units of $L_{\odot}$/A and x-axis units of Angstroms. Thus the y-axis is a luminosity density instead of a flux density. In contrast, observationally, we tend to always work with spectra that have y-axis units of flux density ($F_{\lambda}$ in erg/s/cm$^2$/A or $F_{\nu}$ in erg/s/cm$^2$/Hz). Similarly, spectral energy distributions (SEDs) from photometry tend to have $\lambda F_{\lambda}$ or $\nu F_{\nu}$ such that the y-axis is flux, not flux density.

How do I convert a theoretical template spectrum from units of luminosity density ($L_{\odot}$/A) to flux density (erg/s/cm$^2$/A)?

For context, I want to fit spectral templates to an observed SED. The observed SED is for an object at a redshift $z$, so I think I can either convert the templates to flux density units, or I can convert my observed SED to luminosity density units. I feel like working in flux density units is more natural -- plus I'm not sure if multiplying the observed SED y-axis values by $4\pi D^2$ (D is distance of object) and x-axis (wavelengths) by $1/(1+z)$ would be sufficient (e.g., normalization concerns).


texts: Why do we presume that the universe has always expanded?

texts: When I read about the universe having always expanded from a 'singularity', I can't help but wonder if that is perhaps not the case. If a singularity is a point at which everything is infinite and is, theoretically, impossible, why are we quite so convinced it existed? What evidence is there that the universe didn't start out as a single square centimetre or even perhaps half the size it is now, because weve only known it's been expanding for the last century or so because of technological advances? Perhaps it was sizeable to begin with but the pressure of more atoms forming has pushed it outwards? Probably a ridiculous theory but Im intrigued to hear what others think about the whole subject because I just don't think the current presumption is based on any real evidence and is likely to be totally wrong.


texts: Does our Sun have a counterpart, i.e., is it a part of a binary-system? If so, how does the other star look like and where is it?


texts: Shouldn't the estimate of the universe's age be higher, not lower, after the attractive strength of gravity is taken into account?

texts:
From 'Fundamentals: Ten Keys to Reality', by Frank Wilczek :
"Running the movie of cosmic history backward in our minds, we found the galaxies all coming together to meet at a definite time.  When did it happen?  To calculate how long ago, we simply divide the distance a galaxy must travel by the speed at which it's moving.  (Since a galaxy's speed is proportional to its distance according to Hubble's observations, we'll find the same result consistently whichever galaxy we choose.)  Doing that, we estimate that galaxies were all smushed together about 20 billion years ago.  More accurate calculations, which include how the velocities change over time due to gravity, yield a somewhat smaller result.  Today's best estimate is that 13.8 billion years have elapsed since the big bang."
Since gravity is an attractive force, partially offsetting the expansion of the universe, shouldn't the estimated age be higher than the initial 20 billion years, not lower?
For instance, if astronomers, somehow, discovered that there was even more matter in the universe than estimated, wouldn't that cause them to revise the estimated age of the universe upwards, not downwards?
In other words, with gravity partially resisting and slowing down the expansion, wouldn't it have taken that much longer for the universe to reach its current size?


texts: Any simple experiment with an H-alpha telescope?

texts:
Is there any simple experiment that can be done with an H-alpha telescope, for example to estimate the Sun's mass, size, distance, temperature or intensity?

I give lessons about renewable energy and it would be nice to somehow integrate a telescope (PST Coronado + double stack) to the chapter about photovoltaics and solar thermal energy.

Right now, the only "experiment" I could come up with was to show that there's often nothing to see because of the solar minimum. But we also wouldn't see any feature if the telescope was not focused or not well calibrated.
With some luck, it should be possible to follow the movement of a sunspot over a few days and estimate how fast the sun is rotating, possibly at different latitudes.
I suppose that in order to calculate many sun characteristics, it is mandatory to know the average distance between Earth and the Sun. It seems to be relatively hard to estimate 1 AU.

Is it possible to use the telescope for any experiment and estimate an order of magnitude for any of the Sun characteristics, assuming that the distance to the Sun is approximately 150 000 000km?


texts: I need to know the definition of deep space.  I am an amateur astronomer, and am experiencing some difficulty understanding this.


texts: I know black holes can be described by only a few parameters. Given the extreme conditions within a neutron star, how much hair does it have, ie. how much of the original star parameters and composition (e.g. metallicity) affects the features of a neutron star?


texts: Why does "longitude by chronometer" require first calculating latitude?

texts:
I'm studying the history of longitude and Greenwich Time, and I'm currently confused about the "longitude by chronometer" technique.

Conceptually, the method seems extremely simple.  With a chronometer (ie. an accurate clock) set to the time of your home port, compare to your local time.  Multiply the difference by $\frac{15°}{hour}$ and that will give you the degrees of longitude you have traveled.

According to Derek Howse's Greenwich Time and the Longitude and Dava Sobel's Longitude, this method was first published by Gemma Frisius in 1530, then described again by Richard Eden in 1555.  Both of these authors say that you must first find your latitude.  Here is Frisius in 1530 (emphasis mine):

  We must wait until the hand of our clock exactly touches the point of an hour and at the same moment by means of an astrolabe or by means of our globe, we must find out the time of the place at which we now find ourselves.  If this time agrees to the minute with the time shown on our watch, it is certain that we are still on the same meridian or in the same longitude, and our journey has been made towards the south.  But if it differs by one hour or by a number of minutes, then these should be turned into degrees, or minutes of degrees, by the method I set out in the previous chapter, and in this way the longitude is discovered.  In this way I would be able to find the longitude of places, even if I was dragged off unawares across a thousand miles, and even though the distance of my journey was unknown. But then first of all, as always, the latitude must be learnt.  I have already explained this before and also that it can be found out by various methods of finding out the tirne.

Here is Eden in 1555:

And so shall the longitude bee found.  And by
   this arte can I fynde the longitude of
       regions althowgh I were a thou-
        sand myles owt of my attempt-
         ted course & in an unkno-
           wen distance, but the
            latitude must fyrst
               bee perfectly
                  knowen.

I can't figure out why knowing the latitude would be necessary for calculating longitude by chronometer, unless you need it to calculate the local time.  But it seems to be well established that local time can be easily calculated with a noon sighting of the Sun, corrected for the equation of time.  This method is described here.

Most of the Wikipedia page for Longitude by Chronometer seems to describe a more complicated method that involves finding the intersection of a position line with an assumed latitude.  It also describes solving the navigational triangle.  I'm having trouble following the method described there.  I can't tell whether this is the same method described by Frisius or something else entirely.

So overall my questions are:

Why do Frisius and Eden say that you need to calculate latitude before you can do longitude by chronometer?  Is it just a step in calculating the local time?
What is the method described in the "Longitude by Chronometer" Wikipedia page, and the navigational triangle stuff?  How does it work, and what benefit does it have over the simple $(t_{home} - t_{local})\frac{15°}{hour}$ method?


texts: How could the universe be a few light years across just 1 second after the big bang?

texts:
I was skimming through Neil deGrasse Tyson's book Astrophysics for People in a Hurry when I noticed he says something curious on page 26:

"By now, one second of time has passed [since the big bang]. The universe has grown a few light years across."

How could the universe have expanded to a few light years in diameter in just one second if nothing can travel than light? By definition of a light year, wouldn't take a 1+ years for the universe to get this big?


texts: What is a hypernova and have we observed any?

texts:
Inspired by the question "What does it mean for a star to go nova or supernova? Can I safely observe these?", I am curious about what hypernovas are?

Have we observed any occurring, or the at least the after-effects?

Is there an upper limit of how large a stellar explosion can be?


texts: How to calculate the frequency of a gas giant eclipsing the sun from a moon?

texts: Say you have a moon around a gas giant which goes around a star. If the moon has an inclination of around 0° relative to the gas giant's orbit, the gas giant will eclipse the star every orbit of the moon. However, if the inclination is somewhat larger than 0°, not every orbit of the moon will contain a planetary eclipse. How would you calculate the amount of moon orbits in a row with a planetary eclipse?


texts: What maintains the high orbital eccentricity of many exo-planets near their sun?

texts:
Over the last decade we've discovered that many exoplanets not only have highly eccentric orbits, but also orbit very close to their sun. This is true of many classes of stars.

I definitely have a gap in my understanding, because I'm perplexed as to why the orbits don't circularize when the planets are so close to their star. The tidal forces can be immense, yet the proportionally large number of eccentric planets indicates that many are likely not circularizing (at least over time periods of a handful of giga years).

Why?

I don't understand the physics of this well enough to say. Could it have something to do with with spin-orbital resonance of the planet? A paper I found from Anthony R. Dobrovolskis titled Spin states and climates of eccentric exoplanets indicates that highly eccentric planets in the tidal-lock zone would likely lock into spin states other than 1:1. This could be 2:1, 3:2, etc. Much like mercury. Does the achievement of this spin-orbital resonance do something to preserve the eccentricity?

I'd appreciate any help that could be provided!

Update:

Because it was asked for, I've included a list of some exoplanets that have both short orbital periods as well as highly eccentric orbits (varying from ≈0.15 all the way up to around 0.5). Ages of systems vary widely or is not known, from possibly as low as about 2gy up to over 10gy.

http://www.openexoplanetcatalogue.com/planet/CoRoT-16%20b/
http://www.openexoplanetcatalogue.com/planet/HD%2011964%20A%20c/
http://www.openexoplanetcatalogue.com/planet/HD%20109271%20c/
http://www.openexoplanetcatalogue.com/planet/HD%2017156%20b/
http://www.openexoplanetcatalogue.com/planet/HD%2017156%20b/
http://www.openexoplanetcatalogue.com/planet/KOI-1299%20b/ - VERY eccentric

Possibly highly eccentric, but measurement delta is too large to confirm eccentricity above ≈0.11:

http://www.openexoplanetcatalogue.com/planet/Kapteyn%20b/

Update 2:

More sources showing the existence of near-orbiting highly eccentric planets. While higher eccentricities are common farther out from a star, it looks like moderately high eccentricities (0.2, 0.3, 0.4) are not infrequent close-in to a star, particularly if the system lacks many other planets. Very high eccentricities are also possible close-in.

From: https://academic.oup.com/mnras/article/425/1/757/1004680

"Eccentricity versus semimajor axis going from low (left) to high multiplicity (right). A red dot is shown for where Jupiter would appear on the one- and two-planet distributions, and for Saturn on the two-planet distribution."


texts: Appearance (frequency) ranking of stars?

texts: Is there some ranking / statistics that shows how common given type of celestial objects is? A table that would allow the answers to questions like: What type of star is most common per volume of our galaxy? Are white dwarfs more common than red giants? What percentage in the number of celestial objects located are the black holes? Pulsars? How many red giants have been catalogued?


texts: Is it possible for a planet to have multiple moons in a nearly stationary orbit?

texts:
I have done a lot of searching online and while I have been able to find out that theoretically a moon could exist in a near-synchronous/stationary orbit, I am wondering if it is possible for multiple moons to exist in this state.

I'm not sure if I've explained appropriately or not, so if this needs to be a little clearer, please let me know.

The purpose of this question is that I am writing a novel and I had this idea that the planet has 9 moons and that the area of land that the story takes place in the moons only travel across the sky over the course of many days.  One moon might take 60 days to get from one horizon to the other, while another might take 15 days, and others would be varying times in between.

In my limited knowledge, I have surmised that a moon closer to the planet would take less time to cross the sky than a moon further away.  Obviously, for this to work, the moons would have to be in a supersynchronous orbit, not fully synchronous.  Would the range of distance for supersynchronous orbits allow multiple moons to exist in staggered distances and still be close enough to remain visible from one spot continuously for multiple days at a time?

Disclaimer:
I am not sure that this is the appropriate place to ask this question, since it is mostly theoretical.  I also want to apologize if my English is confusing.  Finally, weird letters and symbols in math make my head hurt, so I am sorry I cannot follow complicated mathematical formulas, but feel free to post them if you believe it may help answer the question.


texts:
I've read (in Gates to the Hebrew calendar p.128   and other sources) that the Earth orbits the Sun in 365.256 days, but each 1000 years the year becomes shorter by 5.5 seconds.

  "The accurate length of the year is 365 days, 5 hours, 48 minutes, and 45.216 seconds. However this time is going and becoming shorter by 5.5 seconds each 1000 years.

Does this mean that in 10000 years it'll become shorter by 55 seconds, and in 100 years it'll become shorter by 9.16 minutes? What's the explanation for the year shortening with time?

[N.b. I've not read the first book mentioned above and the cite is a translation was presented by a lecturer from which I took notes. Therefore, it could be that the original book contains the explanation. I have no way to check it and that's why I'm seeking here the explanation].


texts:
From my understanding we detect planets by measuring dips in light intensity from the star the habitable planet is orbiting when it passes by it.
There are 2 things I don’t understand about this method:

Planets in a solar system tend to orbit their star in one disc like plane. Can we only detect planets if this plane is in-alignment with our sensors here on earth/ space. I assume if someone looked at our sun from the ‘bottom’ they would never see a planet cross it. If so this would exclude a big portion of the stars we are looking at?
Our orbit is 1 year. I assume the orbits of habitable plants can vary and having a short/ close to 1 year orbit is not a criteria for habitability. Even so we have to measure 1 dip every year or 10. How can we tell that this a planet with a regular yearly orbit or just anything passing between the star and us. So maybe a better question to ask for number 2 is what can we find out from these dips?


texts: How can the 13.8 billion years old universe have a radius of 46 billion light years?

texts: The universe is about 13.8 billion years old. Assume at the big-bang it starts from a small region and the maximum possible speed according Einstein is the speed of light how can the universe got a radius of 46 billion light years? According my understanding it could have a max. radius of 13.8 billion light years only. Can someone explain to a non-astrophysicists.


texts: How many stars are in the Sculptor Dwarf Galaxy?

texts:
The Sculptor Dwarf Galaxy is a small satellite Galaxy of the Milky Way. There are many such satellites galaxies and I'm trying to compile basic data on them.

However, I can't find an estimate for the number of stars in the Sculptor Dwarf (and many other satellite galaxies too). I'm disappointed that Wikipedia doesn't have this basic information, and that makes me suspicious that estimating the number of stars in other galaxies is not very easy or reliable for current astronomy.

Googling these things has resulted in nothing but a bunch of pop science sites...which is no surprise except that these sites don't seem to have the number of stars either. This lack of basic data is surprising and only adds to me worries that no reliable estimates exist.

Can anyone find a link to this info? It would also be very helpful to point me to a database that has the number of stars for all galaxies in the local group, if such a database exists.


texts: Will Pi have the same value on the surface of say Jupiter, compared to the value of PI on Earth. Or does Pi vary with gravity?


texts: Does astronomical observing "count" as remote sensing?

texts:
I have long considered astronomical observing as a form of remote sensing, though quite different than typical remote sensing in that many objects observed are not resolved.

I am wondering, though, if the  formal definitions of remote sensing include or exclude astronomical observing (and specifically, observing things outside the solar system)?  And/or are there any resources that can be pointed to that either do or don't call astronomical observing remote sensing?


texts:
I've been reading about the Earth's analemma from Wikipedia, and I am having trouble visualizing one component. Let's build up to my question.

If the Earth had a circular orbit and no axial tilt, the analemma would be a dot.
If the Earth had an eccentric orbit and no axial tilt, the analemma would be a east-west line.
If the Earth had a circular orbit and axial tilt, the analemma would be symmetric figure eight.

My question:  In situation 3, I understand the north-south variation of the symmetric analemma, but I don't understand why there would be symmetric east-west variation.

Why does the Earth's axial tilt create an east-west variation in the analemma?


texts: Did Hubble see a pair of UFOs? (Identify this artifact)

texts:
The image below is this one, found in this group of Hubble space telescope images of the interstellar comet 2I/Borisov (C/2019 Q4).

Can anyone recognize this pair of artifacts in the upper right corner of this HST diagnostic image?


texts: Who discovered what set of factors is responsible for visibility of celestial bodies on Earth's daytime sky?

texts:
Visibility of a celestial body on the sky during the day depends on a number of factors - if I recall correctly: the body's magnitude, Seeing, Sky brightness, and probably some others I have missed.

Who was the first to discover/compile the set of variables responsible for determining, whether a celestial body remains visible with naked eye in certain (daylight) conditions?


texts: What telescope is this, and how does it work?

texts:
In the excellent chemistry series of Periodic Videos' episode Amazing piece of metal (speculum) there is an interesting showing and discussion of Isaac Newton's first telescope.

At 02:36 there is a short cut to a view of a very large, modern telescope mirror. I'm confused by the image because it seems to show what looks like a small 45 degree elliptical, diagonal secondary mirror that you might see near the top end of a long focal length Newtonian telescope, except that it seems to be sitting in front of the primary, facing towards the stars.

Can anyone identify this telescope, and help me understand the basics of how this particular optical system is configured?

edit: I was so focused on the small mirror in the center that I neglected to read the caption. This "very large telescope" may in fact be THE Very Large Telescope, one of it's components at least. But because of all the shiny metal an reflections in mirrors, I still don't really understand what I'm looking at as far as the optical system is configured.

https://www.youtube.com/watch?v=4ESW_NTIhBM


texts: How can you find the distance to a galaxy using right ascension and declination?

texts: For example, Galaxy NGC 3689 has the right ascension of 11:28:11 and declination of +25:39:40.0. Using these values, how can we find the distance to the galaxy? If it helps, its radial velocity is 2727 km/s.


texts: Is there any scientific correlation between cold nights and star-lit skies?

texts:
I've many times heard expressions such "cold, starry nights". It's apparently poetic to describe star-lit night skies as being "cold".
Is this based on reality in some way? Is there something about cold weather which would make the stars more visible from Earth?
I've been taking many nightly walks and, maybe, I'd say that the stars seem to be more visible when it's cold/winter. But I'm far from sure about that; it's useless as "evidence". I don't really see why this would be. Seems like it would have more to do with how cloudy it is.


texts: Does the loss of mass create an observable change in a comet's orbit?

texts: Comets lose their mass through water evaporation due to close encounter with sun, so my question is does the loss of mass create an observable change in a comet's orbit? What kind of change that may be shrinking orbit or expanding orbit?


texts: Energy of a charged particle in the magnetosphere

texts:
I asked this question on physics.stackexchange, but as it is a space/magnetosphere question maybe someone here can help me out:

Taking the earth as an idealized dipole and the E field from the sun uniform (at least for a few earth radii) can the energy of particles at distinct radii from earth, in the equatorial plane, be compared as just the fall off of the B field? For example, a particle at geosynchronous orbit and one twice as far away. Would the difference in their energy just be: $\frac{1}{2^{3}}=\frac{1}{8}$ as the E field is constant and contributes equally to each?
To be clear Im using:
$$\Delta KE\propto \Delta B_{r_0}=\frac{\mu_0 M_E}{4\pi}\frac{1}{r_0^3}[r2\cos\theta + \theta\sin\theta]$$


texts: Might Oort cloud comets be exchanged between solar systems?

texts: Considering their distance from their parent stars, might Oort cloud object such as comets be exchanged between passing stars (assuming that other stars have similar Oort clouds)?


texts: What would the cost be of visiting an asteroid?

texts: I'm trying to think through what the cost would be of an unmanned mission to a nearby asteroid.  To me it seems like the high-level costs would be the fixed cost of the "spaceship" itself (including any scientific or mining equipment required to carry out the mission), the cost of getting into orbit which would depend on the ship mass, and the fuel to get there and return (which would be a function of fuel cost, ship mass, how fast you want to get there, and the mass of anything collected at the asteroid site that would be returned).  Is there anywhere that this is discussed or has anyone thought this through further?


texts: Telescope light gathering power and resolution

texts:
I'm a little confused. Could you help me?

The question is;
If we increase the radius of a telescope twice, how much does the light gathering power change? What about resolution?

Is it increase 2^2?
For second part i know As the diameter of the telescope's objective increases, the resolving power increases.

Thanks


texts: Does a week represent something in astronomy?

texts:
I know that a day represent the time for the earth to make a full rotation around its own axis and a year is the time for the earth to make a full rotation around the sun.

But does a week represent something? And a month?

Thank you.

ps: Not sure what tags I need to use, feel free to add/remove them


texts: Examples of astrophysical objects NOT in virial equilibrium?

texts:
Astronomers always talk about astrophysical objects being in virial equilibrium (e.g., a stellar system, or a disk of gas within a galaxy, etc.). But I never hear about thermodynamical equilibrium.

What are some examples of objects that are not in virial equilibrium?

One example question: suppose that what you thought was a disk of rotating gas within a galaxy (as revealed by spectroscopy) is actually a bipolar outflow of gas. Would the bipolar outflow of gas be in virial equilibrium?

Is a radio jet (length of hundreds of kpc) from a supermassive black hole in virial equilibrium?


texts: Does the Abell 1689 supercluster have angular momentum?

texts:
The Abell 1689 is a large group of galaxies, containing a lot of elliptical galaxies :

https://en.wikipedia.org/wiki/Abell_1689

Usually, an elliptical galaxy don't have large angular momentum around its center of mass (spin angular momentum, if you prefer).

My question is about the galactic group, globally as a whole.  Does it have angular momentum around its center of mass, or should it be negligible ?


texts:
How can I adjust the axis labels in ds9?

I'd like to have something like:

So far I only managed to get floating points (tl h%f3):

or the leading hours are missing (tl h%f1 m):

Edit:

I tried "tlhm.1" as kindly suggested by Jeremy, but unfortunatly it still does not work:


texts: What are other names for planetoids that aren't orbiting a solar system, but hurtling through space?

texts: I'm trying to think of a good word for an asteroid/planetoid that has no stable orbit but has been ejected from a system and is passing close to a sun. Any help?


texts: Is there an orbit that could cause regular debris showers like in the movie Gravity?

texts:
[some spoilers]

If you were in the ISS and orbiting the Earth roughly every 90 minutes, would it be possible for debris to be orbiting such that it passes you every 90 minutes?

While Neil DeGrass Tyson pointed out scientific flaws in the movie on twitter, he praised many things the movie got right in interviews, including "The 90-minute orbital time for objects at that altitude."  I think I recall an interview on a podcast that I can't remember where he specifically said that referring to the debris recurring every 90 minutes.

In reality wouldn't the debris have to be in a different orbit?  If the ISS orbits every 90 minutes (92.87 really but I'm saying 90) then after 90 minutes they would be in the same relative position.  The Earth would have rotated in the mean time so they wouldn't be over the same point on Earth, but they would be in the same position in orbit about the Earth.  Is there an orbit that would allow the same debris to cross the same spot in their orbit every 90 minutes?  Would it be nearly the same orbit, just inclined slightly?  Would that explain why the debris was moving so slowly relative to the ISS as well?

note:

There are problems with the orbits and location in the movie, I simplified my question to ask about the particular orbit of the ISS.


texts: Are micrometeorites just dust grains at high relative speed, or is there some difference between them and cosmic or interstellar or solar nebula dust? Dust as in the clouds which obscure parts of the Milky Way in our night sky.


texts: Is it unlikely for a meteor to hit the day side of the earth?

texts:
I have binge watched a lot of documentaries and movies about meteors hitting the earth. The one pattern I have seen, even in the science-fact documentaries like Nova, is that the animations show meteors hitting the earth on the day side. By that, I mean at a near 90° angle in the center of the day zone. As if it were to hit the earth at high noon.

What seems unlikely to me is where the meteor hits. It seems intuitive to me that statistics would favor a meteor strike on the night side of the planet rather than the day side. Or, possibly from the transition between day and night if the meteor came in from the side.

Is my suspicion correct? Is it unlikely for a meteor to hit the earth on the day side and far more likely to hit the night side?

To clarify, I'm thinking of significant meteor strike, like the Chicxulub impact  that killed off the dinosaurs. If something that massive came in from the day side, wouldn't it more likely to have been captured or redirected by the sun because of the sun's gravity?


texts: Laser Collimator For Dobsonian vs Newtonian

texts: Will a laser collimator like the Gosky 1.25 Metal Laser Collimator, https://www.amazon.com/gp/product/B01M4IVUYG/ref=crt_ewc_title_dp_1?ie=UTF8&psc=1&smid=AHQ6VCR020F8X, work for a dobsonian even though it says it's for a newtonian?


texts: At the Big Bang, when everything was close together, why did it not "collide", violating Planck length or Pauli Exclusion Principle?

texts: How could so much matter, or "all" in fact, have been concentrated in a smaller universe without being in the actual same place? Why did this not result in undercutting the Planck Length or violating the Pauli exclusion principle?


texts: Is Higgs Boson mass equal to the missing mass of dark matter?

texts:
Sorry if this is a very lay question. I am just an armchair physicist.

The Higgs Boson was just recently discovered, and it has a mass which is considerably larger than a proton. If this Higgs Boson was just recently discovered and the Higgs Boson is EVERYWHERE (ie. The Higgs Field), why wouldn't this perfectly explain the missing mass that is "dark matter" ?


texts: Which focus point does the sun occupy for each planet?

texts:
I am aware that planets orbit in an elliptical fashion and that the sun occupies one of two focal points.

Let us say that the left focal point is f1 and the right f2.

Is the sun at the same focal point for each planet?

If not which ones are different?


texts:
consider two stars of the spectral type and subtype, but not necessarily both on the main sequence. Describe whether this information is sufficient to tell you how the stars differ in surface temperature, size, and distance?

so if they have they same spectral type and subtype i think they're supposed to have the same surface temperature. however this is not enough information to tell us about their sizes and distances. is this correct? any insight would be great, thanks!


texts: Warm and Hot dark matter density profiles

texts:
For cold dark matter, density profiles are well known and easy to find information about - eg. NFW, Burkert, Einasto, and others.

But for some reason I couldn't find explicit expressions for the density profiles for Hot and Warm dark matter.

I need to know what are $\rho_{_{HDM}}(r)$,$\rho_{_{WDM}}(r)$.

I'm interested in the differences between cold/hot/warm dark matter and why do we use Cold dark matter ($\Lambda$-CMD  model) and not Hot or Cold dark matter. I need to back my claims with formal quantitative analysis and not just a qualitative explanation.

If you can recommend about other aspects which differentiate the models, or a good review paper on the subject, I would welcome it.


texts: Where can I find Arecibo's data archive?

texts: Does anyone know where I can find Arecibo's historical data? After much searching, I can find neither hide nor hair of it. It doesn't help that the search results are completely dominated by the news of the relatively recent collapse of the telescope and I didn't come up with anything through their Science Portal.


texts: How big would the asteroid belt planet be?

texts:
As I understand it, the asteroid belt exists because the gravitational force of Jupiter prevents the asteroids from accreting (is that a word?) into a planet.

If, however, Jupiter didn't exist and they did create a planet, how big would that planet be?


texts: Calculate apsides without knowing eccentricity

texts: How would one go about determining the apsides of an orbit, knowing only the current distance between the 2 bodies, the orbital velocity, and the period? Every formula I've seen requires eccentricity, but conveniently, every formula for eccentricity requires the apsides. Surely there must be some way to find one without knowing the other?